Interferential position-measuring devices based on the scanning of scales having optical diffraction gratings are described, for example, in the European Patent No. 0 163 362.
A position-measuring device based on scales having grating structures and optical scanning is also described in PCT International Published Patent Application No. WO 2007/034379. However, the position-measuring device described in PCT International Published Patent Application No. WO 2007/034379 has the disadvantage that partial beams of different direction reflected at a deflecting element do not travel in parallel to the detector, and therefore their point of incidence at the detector is dependent on the distance of the deflecting element from the detector.